Lubricating composition

ABSTRACT

Use of a nitrogen-containing ashless dispersant in a lubricating composition for the purpose of reducing wear in the presence of ZDTP and soot wherein the nitrogen-containing ashless dispersant has a Functionality (F) of greater than 1.4.

FIELD OF THE INVENTION

The present invention relates to a lubricating oil composition, in particular to a lubricating oil composition which is suitable for lubricating internal combustion engines and which has reduced wear properties.

BACKGROUND OF THE INVENTION

Increasingly severe automobile regulations in respect of emissions and fuel efficiency are placing increasing demands on both engine manufacturers and lubricant formulators to provide effective solutions to improve fuel economy.

Optimising lubricants through the use of high performance basestocks and novel additives represents a flexible solution to a growing challenge.

Anti-wear additives are important to mitigate issues arising from the desire to have low viscosity formulations in order to reduce fuel consumption and various such additives are already known in the art.

A common anti-wear additive which is well known for use in lubricating compositions is a zinc dithiophosphate, such as, for example, zinc dialkyl-, diaryl- or alkylaryl-dithiophosphates. Zinc dithiophosphate may be conveniently represented by general formula II:

wherein R² to R⁵ may be the same or different and are each a primary alkyl group containing from 1 to 20 carbon atoms preferably from 3 to 12 carbon atoms, a secondary alkyl group containing from 3 to 20 carbon atoms, preferably from 3 to 12 carbon atoms, an aryl group or an aryl group substituted with an alkyl group, said alkyl substituent containing from 1 to 20 carbon atoms preferably 3 to 18 carbon atoms.

Examples of suitable zinc dithiophosphates which are commercially available include those available ex. Lubrizol Corporation under the trade designations “Lz 1097” and “Lz 1395”, those available ex. Chevron Oronite under the trade designations “OLOA 267” and “OLOA 269R”, and that available ex. Afton Chemical under the trade designation “HITEC 7197”; C9417, zinc dithiophosphates such as that available from Infineum under the tradename Infineum C9417, those available from Lubrizol Corporation under the trade designations “Lz 677A”, “Lz 1095” and “Lz 1371”, that available ex. Chevron Oronite under the trade designation “OLOA 262” and that available ex. Afton Chemical under the trade designation “HITEC 7169”; and zinc dithiophosphates such as those available ex. Lubrizol Corporation under the trade designations “Lz 1370” and “Lz 1373” and that available ex. Chevron Oronite under the trade designation “OLOA 260”.

While zinc dithiophosphate compounds are useful for reducing wear in lubricating compositions, it has been recently found that in the presence of soot, zinc dithiophosphates can lead to an undesirable increase in wear via a newly identified wear mechanism. The wear mechanism of corrosion/abrasion was identified and published in 2010, see Olomolehin, Y., Kapadia, R. G., Spikes, H. A., “Antagonistic interaction of antiwear additives and carbon black.” Trib Letters 37, 49-58, (2009). A more recent paper has recently reaffirmed this mechanism, see Salehi, F. Motamen, D. N. Khaemba, A. Morina, and A. Neville, “Corrosive-Abrasive Wear Induced by Soot in Boundary Lubrication Regime.” Trib Letters 63, 1-11, (2016).

It would therefore be desirable to find a way to reduce wear of lubricating compositions containing zinc dithiophosphate compounds in the presence of soot.

It has now surprisingly been found that by using certain nitrogen-containing ashless dispersants, a lubricating oil composition can be provided which exhibits reduced wear in the presence of zinc dithiophosphate compounds and soot.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides the use of a nitrogen-containing ashless dispersant in a lubricating composition for the purpose of reducing wear in the presence of zinc dithiophosphate compounds and soot wherein the nitrogen-containing ashless dispersant has a functionality (F) of greater than 1.4.

DETAILED DESCRIPTION OF THE INVENTION

As used herein the term “soot” means a deep black powdery or flaky substance consisting largely of amorphous carbon. Gas-phase soot contains polycyclic aromatic hydrocarbons (PAH). Soot is produced by the incomplete burning of organic matter, such as hydrocarbon based fuels. It consists of agglomerated nanoparticles with diameters between 6 and 30 nm. The soot particles can be mixed with metal oxides and with minerals and can be coated with sulfuric acid. In the context of an internal combustion engine, soot can travel from the combustion chamber into the lubricant and can accumulate in the lubricant.

In the context of the present invention, the amount of soot in the lubricating composition containing the zinc dithiophosphate compound is typically at a level of from 0.1 wt % to 10 wt %. In one embodiment, the level of soot is from 2 to 7 wt %, by weight of the lubricating composition. In another embodiment, the level of soot is from 3.5 to 7 wt %, by weight of the lubricating composition. In another embodiment, the level of soot is from 5 to 6 wt %, by weight of the lubricating composition.

The nitrogen-containing ashless dispersant is present in the lubricating composition herein at a level so as to provide a level of nitrogen from 0.001 wt % to 0.15 wt %, preferably from 0.05 wt % to 0.1 wt %, by weight of the lubricating composition.

The nitrogen-containing ashless dispersant is used herein to reduce the wear exhibited by a lubricating composition in the presence of zinc dithiophosphate compounds and soot. Hence the term “reducing wear” as used herein means reducing the level of wear to a level below that exhibited by a lubricating composition which contains zinc dithiophosphate and soot but which does not contain the nitrogen-containing ashless dispersant described herein.

In a preferred embodiment herein, the nitrogen-containing ashless dispersant is used to reduce the wear by at least 5%, more preferably by at least 10%, even more preferably by at least 50%, and especially by at least 80%, even more especially by at least 90%, compared with that of an analogous lubricating composition which contains zinc dithiophosphate and soot but which does not contain the nitrogen-containing ashless dispersant described herein.

Suitable dispersants for use herein comprise an oil soluble polymeric long chain backbone having functional groups capable of associating with particles to be dispersed. Typically, such dispersants have amine, amine-alcohol or amide polar moieties attached to the polymer backbone, often via a bridging group. The dispersant may be, for example, selected from oil soluble salts, esters, amino-esters, amides, imides and oxazolines of long chain hydrocarbon-substituted mono- and polycarboxylic acids or anhydrides thereof; thiocarboxylate derivatives of long chain hydrocarbons;

long chain aliphatic hydrocarbons having polyamine moieties attached directly thereto; and Mannich condensation products formed by condensing a long chain substituted phenol with formaldehyde and polyalkylene polyamine.

Generally, each mono- or dicarboxylic acid-producing moiety will react with a nucleophilic group (amine or amide) and the number of functional groups in the polyalkenyl-substituted carboxylic acylating agent will determine the number of nucleophilic groups in the finished dispersant.

PIB Description

The polyalkenyl moiety of the dispersant used in the present invention has a number average molecular weight of from about 700 to about 3000, preferably between 950 and 3000, such as between 950 and 2800, more preferably from about 950 to 2500, and most preferably from about 950 to about 2400. The molecular weight of a dispersant is generally expressed in terms of the molecular weight of the polyalkenyl moiety as the precise molecular weight range of the dispersant depends on numerous parameters including the type of polymer used to derive the dispersant, the number of functional groups, and the type of nucleophilic group employed.

The polyalkenyl moiety from which the high molecular weight dispersants are derived preferably have a narrow molecular weight distribution (MWD), also referred to as polydispersity, as determined by the ratio of weight average molecular weight (M_(w)) to number average molecular weight (Me). Specifically, polymers from which the dispersants used in the present invention are derived have a M_(w)/M_(n) of from about 1.5 to about 2.0, preferably from about 1.5 to about 1.9, most preferably from about 1.6 to about 1.8.

Suitable hydrocarbons or polymers employed in the formation of the dispersants used in the present invention include homopolymers, interpolymers or lower molecular weight hydrocarbons. One family of such polymers comprise polymers of ethylene and/or at least one C₃ to C₂₈ alpha-olefin having the formula H₂C═CHR¹ wherein R¹ is straight or branched chain alkyl radical comprising 1 to 26 carbon atoms and wherein the polymer contains carbon-to-carbon unsaturation, preferably a high degree of terminal ethenylidene unsaturation. Preferably, such polymers comprise interpolymers of ethylene and at least one alpha-olefin of the above formula, wherein R¹ is alkyl of from 1 to 18 carbon atoms, and more preferably is alkyl of from 1 to 8 carbon atoms, and more preferably still of from 1 to 2 carbon atoms. Therefore, useful alpha-olefin monomers and comonomers include, for example, propylene, butene-1, hexene-1, octene-1, 4-methylpentene-1, decene-1, dodecene-1, tridecene-1, tetradecene-1, pentadecene-1, hexadecene-1, heptadecene-1, octadecene-1, nonadecene-1, and mixtures thereof (e.g., mixtures of propylene and butene-1, and the like). Exemplary of such polymers are propylene homopolymers, butene-1 homopolymers, ethylene-propylene copolymers, ethylene-butene-1 copolymers, propylene-butene copolymers and the like, wherein the polymer contains at least some terminal and/or internal unsaturation. Preferred polymers are unsaturated copolymers of ethylene and propylene and ethylene and butene-1. The interpolymers used herein may contain a minor amount, e.g. 0.5 to 5 mole % of a C₄ to C₁₈ non-conjugated diolefin comonomer. However, it is preferred that the polymers used in the present invention comprise only alpha-olefin homopolymers, interpolymers of alpha-olefin comonomers and interpolymers of ethylene and alpha-olefin comonomers. The molar ethylene content of the polymers employed in this invention is preferably in the range of 0 to 80%, and more preferably 0 to 60%. When propylene and/or butene-1 are employed as comonomer(s) with ethylene, the ethylene content of such copolymers is most preferably between 15 and 50%, although higher or lower ethylene contents may be present.

These polymers may be prepared by polymerizing alpha-olefin monomer, or mixtures of alpha-olefin monomers, or mixtures comprising ethylene and at least one C₃ to C₂₈ alpha-olefin monomer, in the presence of a catalyst system comprising at least one metallocene (e.g., a cyclopentadienyl-transition metal compound) and an alumoxane compound. Using this process, a polymer in which 95% or more of the polymer chains possess terminal ethenylidene-type unsaturation can be provided. The percentage of polymer chains exhibiting terminal ethenylidene unsaturation may be determined by FTIR spectroscopic analysis, titration, or C¹³ NMR. Interpolymers of this latter type may be characterized by the formula POLY-C(R¹)═CH₂ wherein R¹ is C₁ to C₂₆ alkyl, preferably C₁ to C₂₈ alkyl, more preferably C₁ to C₈ alkyl, and most preferably C₁ to C₂ alkyl, (e.g., methyl or ethyl) and wherein POLY represents the polymer chain. The chain length of the R¹ alkyl group will vary depending on the comonomer(s) selected for use in the polymerization. A minor amount of the polymer chains can contain terminal ethenyl, i.e., vinyl, unsaturation, i.e. POLY-CH═CH₂, and a portion of the polymers can contain internal monounsaturation, e.g. POLY-CH═CH(R¹), wherein R¹ is as defined above. These terminally unsaturated interpolymers may be prepared by known metallocene chemistry and may also be prepared as described in U.S. Pat. Nos. 5,498,809; 5,663,130; 5,705,577; 5,814,715; 6,022,929 and 6,030,930.

Another useful class of polymers is polymers prepared by cationic polymerization of isobutene, styrene, and the like. Common polymers from this class include polyisobutenes obtained by polymerization of a C₄ refinery stream having a butene content of about 35 to about 75 mass %, and an isobutene content of about 30 to about 60 mass %, in the presence of a Lewis acid catalyst, such as aluminum trichloride or boron trifluoride. A preferred source of monomer for making poly-n-butenes is petroleum feedstreams such as Raffinate II. These feedstocks are disclosed in the art such as in U.S. Pat. No. 4,952,739. Polyisobutylene is a most preferred backbone herein because it is readily available by cationic polymerization from butene streams (e.g., using AlCl₃ or BF₃ catalysts). Such polyisobutylenes generally contain residual unsaturation in amounts of about one ethylenic double bond per polymer chain, positioned along the chain. A preferred embodiment utilizes polyisobutylene prepared from a pure isobutylene stream or a Raffinate I stream to prepare reactive isobutylene polymers with terminal vinylidene olefins. Preferably, these polymers, referred to as highly reactive polyisobutylene (HR-PIB), have a terminal vinylidene content of at least 65%, e.g., 70%, more preferably at least 80%, most preferably, at least 85%. The preparation of such polymers is described, for example, in U.S. Pat. No. 4,152,499. HR-PIB is known and HR-PIB is commercially available under the tradenames Glissopal™ (from BASF) and Ultravis™ (from BP-Amoco).

Polyisobutylene polymers that may be employed are generally based on a hydrocarbon chain of from about 700 to 3000. Methods for making polyisobutylene are known. Polyisobutylene can be functionalized by halogenation (e.g. chlorination), the thermal “ene” reaction, or by free radical grafting using a catalyst (e.g. peroxide), is described below.

The hydrocarbon or polymer backbone can be functionalized, e.g., with carboxylic acid producing moieties (preferably acid or anhydride moieties) selectively at sites of carbon-to-carbon unsaturation on the polymer or hydrocarbon chains, or randomly along chains using any of the three processes mentioned above or combinations thereof, in any sequence.

Processes for reacting polymeric hydrocarbons with unsaturated carboxylic acids, anhydrides or esters and the preparation of derivatives from such compounds are disclosed in U.S. Pat. Nos. 3,087,936; 3,172,892; 3,215,707; 3,231,587; 3,272,746; 3,275,554; 3,381,022; 3,442,808; 3,565,804; 3,912,764; 4,110,349; 4,234,435; 5,777,025; 5,891,953; as well as EP 0 382 450 B1; CA-1,335,895 and GB-A-1,440,219.

The polymer or hydrocarbon may be functionalized, for example, with carboxylic acid producing moieties (preferably acid or anhydride) by reacting the polymer or hydrocarbon under conditions that result in the addition of functional moieties or agents, i.e., acid, anhydride, ester moieties, etc., onto the polymer or hydrocarbon chains primarily at sites of carbon-to-carbon unsaturation (also referred to as ethylenic or olefinic unsaturation) using the halogen assisted functionalization (e.g. chlorination) process or the thermal “ene” reaction.

Functionalisation

Selective functionalization can be accomplished by halogenating, e.g., chlorinating or brominating the unsaturated α-olefin polymer to about 1 to 8 mass %, preferably 3 to 7 mass % chlorine, or bromine, based on the weight of polymer or hydrocarbon, by passing the chlorine or bromine through the polymer at a temperature of 60 to 250° C., preferably 110 to 160° C., e.g., 120 to 140° C., for about 0.5 to 10, preferably 1 to 7 hours. The halogenated polymer or hydrocarbon (hereinafter backbone) is then reacted with sufficient monounsaturated reactant capable of adding the required number of functional moieties to the backbone, e.g., monounsaturated carboxylic reactant, at 100 to 250° C., usually about 180° C. to 235° C., for about 0.5 to 10, e.g., 3 to 8 hours, such that the product obtained will contain the desired number of moles of the monounsaturated carboxylic reactant per mole of the halogenated backbones. Alternatively, the backbone and the monounsaturated carboxylic reactant are mixed and heated while adding chlorine to the hot material.

While chlorination normally helps increase the reactivity of starting olefin polymers with monounsaturated functionalizing reactant, it is not necessary with some of the polymers or hydrocarbons contemplated for use in the present invention, particularly those preferred polymers or hydrocarbons which possess a high terminal bond content and reactivity. Preferably, therefore, the backbone and the monounsaturated functionality reactant, e.g., carboxylic reactant, are contacted at elevated temperature to cause an initial thermal “ene” reaction to take place. Ene reactions are known.

The hydrocarbon or polymer backbone can be functionalized by random attachment of functional moieties along the polymer chains by a variety of methods. For example, the polymer, in solution or in solid form, may be grafted with the monounsaturated carboxylic reactant, as described above, in the presence of a free-radical initiator. When performed in solution, the grafting takes place at an elevated temperature in the range of about 100 to 260° C., preferably 120 to 240° C. Preferably, free-radical initiated grafting would be accomplished in a mineral lubricating oil solution containing, e.g., 1 to 50 mass %, preferably 5 to 30 mass % polymer based on the initial total oil solution.

The free-radical initiators that may be used are peroxides, hydroperoxides, and azo compounds, preferably those that have a boiling point greater than about 100° C. and decompose thermally within the grafting temperature range to provide free-radicals. Representative of these free-radical initiators are azobutyronitrile, 2,5-dimethylhex-3-ene-2, 5-bis-tertiary-butyl peroxide and dicumene peroxide. The initiator, when used, typically is used in an amount of between 0.005% and 1% by weight based on the weight of the reaction mixture solution. Typically, the aforesaid monounsaturated carboxylic reactant material and free-radical initiator are used in a weight ratio range of from about 1.0:1 to 30:1, preferably 3:1 to 6:1. The grafting is preferably carried out in an inert atmosphere, such as under nitrogen blanketing. The resulting grafted polymer is characterized by having carboxylic acid (or ester or anhydride) moieties randomly attached along the polymer chains: it being understood, of course, that some of the polymer chains remain ungrafted. The free radical grafting described above can be used for the other polymers and hydrocarbons used in the present invention.

The preferred monounsaturated reactants that are used to functionalize the backbone comprise mono- and dicarboxylic acid material, i.e., acid, anhydride, or acid ester material, including (i) monounsaturated C₄ to C₁₀ dicarboxylic acid wherein (a) the carboxyl groups are vicinyl, (i.e., located on adjacent carbon atoms) and (b) at least one, preferably both, of said adjacent carbon atoms are part of said mono unsaturation; (ii) derivatives of (i) such as anhydrides or C₁ to C₅ alcohol derived mono- or diesters of (i); (iii) monounsaturated C₃ to C₁₀ monocarboxylic acid wherein the carbon-carbon double bond is conjugated with the carboxy group, i.e., of the structure —C═C—CO—; and (iv) derivatives of (iii) such as C₁ to C₅ alcohol derived mono- or diesters of (iii). Mixtures of monounsaturated carboxylic materials (i)-(iv) also may be used. Upon reaction with the backbone, the monounsaturation of the monounsaturated carboxylic reactant becomes saturated. Thus, for example, maleic anhydride becomes backbone-substituted succinic anhydride, and acrylic acid becomes backbone-substituted propionic acid. Exemplary of such monounsaturated carboxylic reactants are fumaric acid, itaconic acid, maleic acid, maleic anhydride, chloromaleic acid, chloromaleic anhydride, acrylic acid, methacrylic acid, crotonic acid, cinnamic acid, and lower alkyl (e.g., C₁ to C₄ alkyl) acid esters of the foregoing, e.g., methyl maleate, ethyl fumarate, and methyl fumarate.

To provide the required functionality, the monounsaturated carboxylic reactant, preferably maleic anhydride, typically will be used in an amount ranging from about equimolar amount to about 100 mass % excess, preferably 5 to 50 mass % excess, based on the moles of polymer or hydrocarbon. Unreacted excess monounsaturated carboxylic reactant can be removed from the final dispersant product by, for example, stripping, usually under vacuum, if required.

Derivatisation

The functionalized oil-soluble polymeric hydrocarbon backbone is then derivatized with a nitrogen-containing nucleophilic reactant, such as an amine, amino-alcohol, amide, or mixture thereof, to form a corresponding derivative. Amine compounds are preferred. Useful amine compounds for derivatizing functionalized polymers comprise at least one amine and can comprise one or more additional amine or other reactive or polar groups. These amines may be hydrocarbyl amines or may be predominantly hydrocarbyl amines in which the hydrocarbyl group includes other groups, e.g., hydroxy groups, alkoxy groups, amide groups, nitriles, imidazoline groups, and the like. Particularly useful amine compounds include mono- and polyamines, e.g., polyalkene and polyoxyalkylene polyamines of about 2 to 60, such as 2 to 40 (e.g., 3 to 20) total carbon atoms having about 1 to 12, such as 3 to 12, preferably 3 to 9, most preferably form about 6 to about 7 nitrogen atoms per molecule. Mixtures of amine compounds may advantageously be used, such as those prepared by reaction of alkylene dihalide with ammonia. Preferred amines are aliphatic saturated amines, including, for example, 1,2-diaminoethane; 1,3-diaminopropane; 1,4-diaminobutane; 1,6-diaminohexane; polyethylene amines such as diethylene triamine; triethylene tetramine; tetraethylene pentamine; and polypropyleneamines such as 1,2-propylene diamine; and di-(1,2-propylene)triamine. Such polyamine mixtures, known as PAM, are commercially available. Particularly preferred polyamine mixtures are mixtures derived by distilling the light ends from PAM products. The resulting mixtures, known as “heavy” PAM, or HPAM, are also commercially available. The properties and attributes of both PAM and/or HPAM are described, for example, in U.S. Pat. Nos. 4,938,881; 4,927,551; 5,230,714; 5,241,003; 5,565,128; 5,756,431; 5,792,730; and 5,854,186.

Other useful amine compounds include: alicyclic diamines such as 1,4-di(aminomethyl) cyclohexane and heterocyclic nitrogen compounds such as imidazolines. Another useful class of amines is the polyamido and related amido-amines as disclosed in U.S. Pat. Nos. 4,857,217; 4,956,107; 4,963,275; and 5,229,022. Also usable is tris(hydroxymethyl)amino methane (TAM) as described in U.S. Pat. Nos. 4,102,798; 4,113,639; 4,116,876; and UK 989,409. Dendrimers, star-like amines, and comb-structured amines may also be used. Similarly, one may use condensed amines, as described in U.S. Pat. No. 5,053,152. The functionalized polymer is reacted with the amine compound using conventional techniques as described, for example, in U.S. Pat. Nos. 4,234,435 and 5,229,022, as well as in EP-A-208,560.

Preferred Dispersants

A preferred dispersant for use herein is one comprising at least one polyalkenyl succinimide, which is the reaction product of a polyalkenyl substituted succinic anhydride (e.g., PIBSA) and a polyamine (PAM) that has a coupling ratio of from about 0.65 to about 1.25, preferably from about 0.8 to about 1.1, most preferably from about 0.9 to about 1. In the context of this disclosure, “coupling ratio” may be defined as a ratio of the number of succinyl groups in the PIBSA to the number of primary amine groups in the polyamine reactant.

Another class of high molecular weight ashless dispersants comprises Mannich base condensation products. Generally, these products are prepared by condensing about one mole of a long chain alkyl-substituted mono- or polyhydroxy benzene with about 1 to 2.5 moles of carbonyl compound(s) (e.g., formaldehyde and paraformaldehyde) and about 0.5 to 2 moles of polyalkylene polyamine, as disclosed, for example, in U.S. Pat. No. 3,442,808. Such Mannich base condensation products may include a polymer product of a metallocene catalyzed polymerization as a substituent on the benzene group, or may be reacted with a compound containing such a polymer substituted on a succinic anhydride in a manner similar to that described in U.S. Pat. No. 3,442,808. Examples of functionalized and/or derivatized olefin polymers synthesized using metallocene catalyst systems are described in the publications identified supra.

The preferred dispersants for use herein have a Functionality (F) of greater than 1.4, more preferably greater than 1.5, such as from about 1.5 to about 2.2, more preferably from about 1.5 to about 2.0 or from about 1.5 to about 1.9. Functionality (F) can be determined according to the following formula:

F=(SAP×M _(n))/((1122×A.I.)−(SAP×MW))  (1)

wherein SAP is the saponification number (i.e., the number of milligrams of KOH consumed in the complete neutralization of the acid groups in one gram of the succinic-containing reaction product, as determined according to ASTM D94); M_(n) is the number average molecular weight of the starting olefin polymer (polybutene); A.I. is the percent active ingredient of the succinic-containing reaction product (the remainder being unreacted polybutene and diluent); and MW is the molecular weight of the dicarboxylic acid-producing moiety (98 for maleic anhydride). Generally, each dicarboxylic acid-producing moiety (succinic group) will react with a nucleophilic group (polyamine moiety) and the number of succinic groups in the PIBSA will determine the number of nucleophilic groups in the finished dispersant.

Polymer molecular weight, specifically M_(n), can be determined by various known techniques. One convenient method is gel permeation chromatography (GPC), which additionally provides molecular weight distribution information (see W. W. Yau, J. J. Kirkland and D. D. Bly, “Modern Size Exclusion Liquid Chromatography”, John Wiley and Sons, New York, 1979). Another useful method for determining molecular weight, particularly for lower molecular weight polymers, is vapor pressure osmometry (see, e.g., ASTM D3592).

Suitable hydrocarbons or polymers employed in the formation of the dispersants include polymers prepared by cationic polymerization of isobutene. Common polymers from this class include polyisobutenes obtained by polymerization of a C₄ refinery stream having a butene content of about 35 to about 75% by wt., and an isobutene content of about 30 to about 60% by wt., in the presence of a Lewis acid catalyst, such boron trifluoride (BF₃). Preferably, the polyisobutylene is prepared from a pure isobutylene stream or a Raffinate I stream to prepare reactive isobutylene polymers with terminal vinylidene olefins. Preferably, these polymers, referred to as highly reactive polyisobutylene (HR-PIB), have a terminal vinylidene content of at least 60%, e.g., 70%, more preferably at least 80%, most preferably, at least 85%. The preparation of such polymers is described, for example, in U.S. Pat. No. 4,152,499. Such polymers are conventionally referred to as HR-PIB and HR-PIB is commercially available from Texas Petrochemical Corporation (TPC), or from BASF (under the trade names Glissopal™). Processes for thermally reacting HR-PIB with unsaturated carboxylic acids or anhydrides, and for further reacting the resulting acylating agents (PIBSA) with amines are well known and described, for example, in U.S. Pat. No. 4,152,499 and EP 0 355 895.

To provide the required functionality, the monounsaturated carboxylic reactant, (maleic anhydride), typically will be used in an amount ranging from about 5 to about 300% excess, preferably from about 10 to 200%, such as 20 to 100% excess, based on the moles of polymer. Unreacted excess monounsaturated carboxylic reactant can be removed from the final dispersant product by, for example, stripping, under vacuum, if required.

Polyamines useful in the formation of the dispersants include polyamines having, or having on average, 3 to 8 nitrogen atoms per molecule, preferably from about 5 to about 8 nitrogen atoms per molecule. These amines may be hydrocarbyl amines or may be predominantly hydrocarbyl amines in which the hydrocarbyl group includes other groups, e.g., hydroxy groups, alkoxy groups, amide groups, nitriles, imidazoline groups, and the like. Mixtures of amine compounds may advantageously be used, such as those prepared by reaction of alkylene dihalide with ammonia. Preferred amines are aliphatic saturated amines, including, for example, polyethylene amines such as diethylene triamine; triethylene tetramine; tetraethylene pentamine; and polypropyleneamines such as di-(1,2-propylene)triamine. Such polyamine mixtures, known as PAM, are commercially available. Useful polyamine mixtures also include mixtures derived by distilling the light ends from PAM products. The resulting mixtures, known as “heavy” PAM, or HPAM, are also commercially available. The properties and attributes of both PAM and/or HPAM are described, for example, in U.S. Pat. Nos. 4,938,881; 4,927,551; 5,230,714; 5,241,003; 5,565,128; 5,756,431; 5,792,730; and 5,854,186.

The total amount of base oil incorporated in the lubricating oil composition of the present invention is preferably present in an amount in the range of from 60 to 92 wt. %, more preferably in an amount in the range of from 75 to 90 wt. % and most preferably in an amount in the range of from 75 to 88 wt. %, with respect to the total weight of the lubricating oil composition.

There are no particular limitations regarding the base oil used in the present invention, and various conventional known mineral oils and synthetic oils may be conveniently used.

The base oil used in the present invention may conveniently comprise mixtures of one or more mineral oils and/or one or more synthetic oils.

Mineral oils include liquid petroleum oils and solvent-treated or acid-treated mineral lubricating oils of the paraffinic, naphthenic, or mixed paraffinic/naphthenic type which may be further refined by hydrofinishing processes and/or dewaxing.

Naphthenic base oils have low viscosity index (VI) (generally 40-80) and a low pour point. Such base oils are produced from feedstocks rich in naphthenes and low in wax content and are used mainly for lubricants in which colour and colour stability are important, and VI and oxidation stability are of secondary importance.

Paraffinic base oils have higher VI (generally >95) and a high pour point. Said base oils are produced from feedstocks rich in paraffins, and are used for lubricants in which VI and oxidation stability are important.

Fischer-Tropsch derived base oils may be conveniently used as the base oil in the lubricating oil composition of the present invention, for example, the Fischer-Tropsch derived base oils disclosed in EP-A-776959, EP-A-668342, WO-A-97/21788, WO-00/15736, WO-00/14188, WO-00/14187, WO-00/14183, WO-00/14179, WO-00/08115, WO-99/41332, EP-1029029, WO-01/18156 and WO-01/57166.

Synthetic processes enable molecules to be built from simpler substances or to have their structures modified to give the precise properties required.

Synthetic oils include hydrocarbon oils such as olefin oligomers (PAOs), dibasic acids esters, polyol esters, and dewaxed waxy raffinate. Synthetic hydrocarbon base oils sold by the Royal Dutch/Shell Group of Companies under the designation “XHVI” (trade mark) may be conveniently used.

Preferably, the base oil comprises mineral oils and/or synthetic oils which contain more than 80% wt of saturates, preferably more than 90% wt., as measured according to ASTM D2007.

It is further preferred that the base oil contains less than 1.0 wt. %, preferably less than 0.1 wt. % of sulphur, calculated as elemental sulphur and measured according to ASTM D2622, ASTM D4294, ASTM D4927 or ASTM D3120.

Preferably, the viscosity index of the base fluid is more than 80, more preferably more than 120, as measured according to ASTM D2270.

Preferably, the lubricating oil composition has a kinematic viscosity in the range of from 2 to 80 mm²/s at 100° C., more preferably of from 3 to 70 mm²/s, most preferably of from 4 to 50 mm²/s.

The total amount of phosphorus in the lubricating oil composition of the present invention is preferably in the range of from 0.04 to 0.12 wt. %, more preferably in the range of from 0.04 to 0.09 wt. % and most preferably in the range of from 0.045 to 0.08 wt. %, based on total weight of the lubricating oil composition.

The lubricating oil composition of the present invention preferably has a sulphated ash content of not greater than 2.0 wt. %, more preferably not greater than 1.0 wt. % and most preferably not greater than 0.8 wt. %, based on the total weight of the lubricating oil composition.

The lubricating oil composition of the present invention preferably has a sulphur content of not greater than 1.2 wt. %, more preferably not greater than 0.8 wt. % and most preferably not greater than 0.2 wt. %, based on the total weight of the lubricating oil composition.

The lubricating oil composition of the present invention may further comprise additional additives such as anti-oxidants, anti-wear additives, detergents, dispersants, friction modifiers, viscosity index improvers, pour point depressants, corrosion inhibitors, defoaming agents and seal fix or seal compatibility agents.

Antioxidants that may be conveniently used include those selected from the group of aminic antioxidants and/or phenolic antioxidants.

In a preferred embodiment, said antioxidants are present in an amount in the range of from 0.1 to 5.0 wt. %, more preferably in an amount in the range of from 0.3 to 3.0 wt. %, and most preferably in an amount in the range of from 0.5 to 1.5 wt. %, based on the total weight of the lubricating oil composition.

Examples of aminic antioxidants which may be conveniently used include alkylated diphenylamines, phenyl-α-naphthylamines, phenyl-β-naphthylamines and alkylated α-naphthylamines.

Preferred aminic antioxidants include dialkyldiphenylamines such as p,p′-dioctyl-diphenylamine, p,p′-di-α-methylbenzyl-diphenylamine and N-p-butylphenyl-N-p′-octylphenylamine, monoalkyldiphenylamines such as mono-t-butyldiphenylamine and mono-octyldiphenylamine, bis(dialkylphenyl)amines such as di-(2,4-diethylphenyl) amine and di(2-ethyl-4-nonylphenyl)amine, alkylphenyl-1-naphthylamines such as octylphenyl-1-naphthylamine and n-t-dodecylphenyl-1-naphthylamine, 1-naphthylamine, arylnaphthylamines such as phenyl-1-naphthylamine, phenyl-2-naphthylamine, N-hexylphenyl-2-naphthylamine and N-octylphenyl-2-naphthylamine, phenylenediamines such as N,N′-diisopropyl-p-phenylenediamine and N,N′-diphenyl-p-phenylenediamine, and phenothiazines such as phenothiazine and 3,7-dioctylphenothiazine.

Preferred aminic antioxidants include those available under the following trade designations: “Sonoflex OD-3” (ex. Seiko Kagaku Co.), “Irganox L-57” (ex. Ciba Specialty Chemicals Co.) and phenothiazine (ex. Hodogaya Kagaku Co.).

Examples of phenolic antioxidants which may be conveniently used include C7-C9 branched alkyl esters of 3,5-bis(1,1-dimethyl-ethyl)-4-hydroxy-benzenepropanoic acid, 2-t-butylphenol, 2-t-butyl-4-methylphenol, 2-t-butyl-5-methylphenol, 2,4-di-t-butylphenol, 2,4-dimethyl-6-t-butylphenol, 2-t-butyl-4-methoxyphenol, 3-t-butyl-4-methoxyphenol, 2,5-di-t-butylhydroquinone, 2,6-di-t-butyl-4-alkylphenols such as 2,6-di-t-butylphenol, 2,6-di-t-butyl-4-methylphenol and 2,6-di-t-butyl-4-ethylphenol, 2,6-di-t-butyl-4-alkoxyphenols such as 2,6-di-t-butyl-4-methoxyphenol and 2,6-di-t-butyl-4-ethoxyphenol, 3,5-di-t-butyl-4-hydroxybenzylmercaptooctylacetate, alkyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionates such as n-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, n-butyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate and 2′-ethylhexyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 2,6-d-t-butyl-α-dimethylamino-p-cresol, 2,2′-methylene-bis(4-alkyl-6-t-butylphenol) such as 2,2′-methylenebis(4-methyl-6-t-butylphenol, and 2,2-methylenebis(4-ethyl-6-t-butylphenol), bisphenols such as 4,4′-butylidenebis(3-methyl-6-t-butylphenol, 4,4′-methylenebis(2,6-di-t-butylphenol), 4,4′-bis(2,6-di-t-butylphenol), 2,2-(di-p-hydroxyphenyl)propane, 2,2-bis(3,5-di-t-butyl-4-hydroxyphenyl)propane, 4,4′-cyclohexylidenebis(2,6-t-butylphenol), hexamethyleneglycol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate], triethyleneglycolbis[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate], 2,2′-thio-[diethyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 3,9-bis{1,1-dimethyl-2-[3-(3-t-butyl-4-hydroxy-5-methyl-phenyl)propionyloxy]ethyl}2,4,8,10-tetraoxaspiro[5,5]undecane, 4,4′-thiobis(3-methyl-6-t-butylphenol) and 2,2′-thiobis(4,6-di-t-butylresorcinol), polyphenols such as tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane, 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, bis-[3,3′-bis(4′-hydroxy-3′-t-butylphenyl)butyric acid]glycol ester, 2-(3′,5′-di-t-butyl-4-hydroxyphenyl)methyl-4-(2″,4″-di-t-butyl-3″-hydroxyphenyl)methyl-6-t-butylphenol and 2,6-bis(2′-hydroxy-3′-t-butyl-5′-methylbenzyl)-4-methylphenol, and p-t-butylphenol-formaldehyde condensates and p-t-butylphenol-acetaldehyde condensates.

Preferred phenolic antioxidants include those available under the following trade designations: “Irganox L-135” (ex. Ciba Specialty Chemicals Co.), “Yoshinox SS” (ex. Yoshitomi Seiyaku Co.), “Antage W-400” (ex. Kawaguchi Kagaku Co.), “Antage W-500” (ex. Kawaguchi Kagaku Co.), “Antage W-300” (ex. Kawaguchi Kagaku Co.), “Irganox L109” (ex. Ciba Speciality Chemicals Co.), “Tominox 917” (ex. Yoshitomi Seiyaku Co.), “Irganox L115” (ex. Ciba Speciality Chemicals Co.), “Sumilizer GA80” (ex. Sumitomo Kagaku), “Antage RC” (ex. Kawaguchi Kagaku Co.), “Irganox L101” (ex. Ciba Speciality Chemicals Co.), “Yoshinox 930” (ex. Yoshitomi Seiyaku Co.).

The lubricating oil composition of the present invention may comprise mixtures of one or more phenolic antioxidants with one or more aminic antioxidants.

In a preferred embodiment, the lubricating oil composition may comprise a single zinc dithiophosphate or a combination of two or more zinc dithiophosphates as anti-wear additives, the or each zinc dithiophosphate being selected from zinc dialkyl-, diaryl- or alkylaryl-dithiophosphates.

The zinc dithiophosphate compounds are present in the lubricating composition in an amount so as to provide preferably from 0.01 wt % to 0.16 wt %, more preferably from 0.06% to 0.12%, by weight of the lubricating composition, of phosphorus.

Zinc dithiophosphate is a well known additive in the art and may be conveniently represented by general formula II;

wherein R² to R⁵ may be the same or different and are each a primary alkyl group containing from 1 to 20 carbon atoms preferably from 3 to 12 carbon atoms, a secondary alkyl group containing from 3 to 20 carbon atoms, preferably from 3 to 12 carbon atoms, an aryl group or an aryl group substituted with an alkyl group, said alkyl substituent containing from 1 to 20 carbon atoms preferably 3 to 18 carbon atoms.

Zinc dithiophosphate compounds in which R² to R⁵ are all different from each other can be used alone or in admixture with zinc dithiophosphate compounds in which R² to R⁵ are all the same.

Preferably, the or each zinc dithiophosphate used in the present invention is a zinc dialkyl dithiophosphate. Examples of suitable zinc dithiophosphates which are commercially available include those available ex. Lubrizol Corporation under the trade designations “Lz 1097” and “Lz 1395”, those available ex. Chevron Oronite under the trade designations “OLOA 267” and “OLOA 269R”, and that available ex. Afton Chemical under the trade designation “HITEC 7197”; zinc dithiophosphates such as that available from Infineum under the trade name Infineum C9417, those available ex. Lubrizol Corporation under the trade designations “Lz 677A”, “Lz 1095” and “Lz 1371”, that available ex. Chevron Oronite under the trade designation “OLOA 262” and that available ex. Afton Chemical under the trade designation “HITEC 7169”; and zinc dithiophosphates such as those available ex. Lubrizol Corporation under the trade designations “Lz 1370” and “Lz 1373” and that available ex. Chevron Oronite under the trade designation “OLOA 260”.

The lubricating oil composition according to the present invention may generally comprise in the range of from 0.4 to 1.2 wt. % of zinc dithiophosphate, based on total weight of the lubricating oil composition.

Additional or alternative anti-wear additives may be conveniently used in the composition of the present invention.

Typical detergents that may be used in the lubricating oil of the present invention include one or more salicylate and/or phenate and/or sulphonate detergents.

However, as metal organic and inorganic base salts which are used as detergents can contribute to the sulphated ash content of a lubricating oil composition, in a preferred embodiment of the present invention, the amounts of such additives are minimised.

Furthermore, in order to maintain a low sulphur level, salicylate detergents are preferred.

Thus, in a preferred embodiment, the lubricating oil composition of the present invention may comprise one or more salicylate detergents.

In order to maintain the total sulphated ash content of the lubricating oil composition of the present invention at a level of preferably not greater than 2.0 wt. %, more preferably at a level of not greater than 1.0 wt. % and most preferably at a level of not greater than 0.8 wt. %, based on the total weight of the lubricating oil composition, said detergents are preferably used in amounts in the range of 0.05 to 20.0 wt. %, more preferably from 1.0 to 10.0 wt. % and most preferably in the range of from 2.0 to 5.0 wt. %, based on the total weight of the lubricating oil composition.

Furthermore, it is preferred that said detergents, independently, have a TBN (total base number) value in the range of from 10 to 500 mg·KOH/g, more preferably in the range of from 30 to 350 mg·KOH/g and most preferably in the range of from 50 to 300 mg·KOH/g, as measured by ISO 3771.

Examples of viscosity index improvers which may be conveniently used in the lubricating oil composition of the present invention include the styrene-butadiene copolymers, styrene-isoprene stellate copolymers and the polymethacrylate copolymer and ethylene-propylene copolymers. Such viscosity index improvers may be conveniently employed in an amount in the range of from 1 to 20 wt. %, based on the total weight of the lubricating oil composition.

Polymethacrylates may be conveniently employed in the lubricating oil compositions of the present invention as effective pour point depressants.

Furthermore, compounds such as alkenyl succinic acid or ester moieties thereof, benzotriazole-based compounds and thiodiazole-based compounds may be conveniently used in the lubricating oil composition of the present invention as corrosion inhibitors.

Compounds such as polysiloxanes, dimethyl polycyclohexane and polyacrylates may be conveniently used in the lubricating oil composition of the present invention as defoaming agents.

Compounds which may be conveniently used in the lubricating oil composition of the present invention as seal fix or seal compatibility agents include, for example, commercially available aromatic esters.

The lubricating compositions herein may be conveniently prepared using conventional formulation techniques by admixing base oil with the liquid crystal compound and one or more additives at a temperature of 60° C.

The present invention is described below with reference to the following Examples, which are not intended to limit the scope of the present invention in any way.

EXAMPLES

Various lubricating compositions were prepared by combining a base oil (GTL 4, a Fischer-Tropsch derived base oil having a kinematic viscosity at 100° C. of approximately 4 cSt, available from Shell) with ZDTP. The ZDTP was added in an amount so as to provide 0.08 wt % phosphorus in the final lubricating composition. The formulations also contained a nitrogen-containing ashless dispersant (designated as D1, D2, D3 or D4 in Table 1 below) in varying amounts to give lubricating compositions having varying amounts of nitrogen (0.05 wt % N, 0.07 wt % N or 0.1 wt % N, by weight of the final lubricating compositions). Carbon black was also added to the lubricating compositions in an amount of 5 wt %, by weight of the final lubricating compositions, in order to simulate the effect of the presence of soot in the lubricant.

The nitrogen-containing ashless dispersants used in the present examples were polyisobutylene succinimides having the properties listed below in Table 1:

TABLE 1 Dispersant Functionality Maleation Number PIB Mn (Fv) method Borated D1 2225 1.3 chloro No D2 2300 1.4 Thermal No D3 2225 1.5 Chloro No D4 2300 1.8 thermal No

HFRR Wear Test

The lubricant formulations were subjected to a HFRR wear test. The HFRR (High-Friction Reciprocating Rig) is a controlled reciprocating friction and wear testing device employed to assess the performance of fuels and lubricants. The test uses a 6 mm diameter steel ball loaded and reciprocated against the flat surface of a stationary steel disc immersed in lubricant. At the end of each test, the ball and disc were removed from the test rig, rinsed with toluene and iso-propanol, and then treated with a 0.05 wt % solution of ethylenediaminetetraacetic acid (EDTA) for 60 s. This was to remove any ZDTP anti-wear film on the surfaces since it can interfere with optically-based wear measurement. Topography images were then obtained and analysed to determine wear volumes of the wear scars on the ball and the disc using the SWLI Veeco Wyko model NT9100. The instrument was set in Vertical Scanning Interferometry (VSI) mode, calibrated to measure rough surfaces with a nanometre detection range.

The results of these wear tests are shown in Table 2 below.

TABLE 2 HFRR Wear Volume (μm³) Dispersant 0.05% N 0.07% N 0.1% N D1 640818 367829 254700 D2 475946 402865 387829 D3 26865 28355 30466 D4 21960 20987 20412

DISCUSSION

From the results in Table 2 it can be seen that the formulations containing the polyisobutylene succinimide dispersants D3 and D4 (having functionality values of 1.5 and 1.8, respectively), demonstrated reduced wear (low wear scar measurements) compared with the formulations containing the polyisobutylene succinimide dispersants D1 and D2 (having Functionality Values Fv of 1.3 and 1.4, respectively). 

1. A lubricating composition for the purpose of reducing wear in the presence of a zinc dithiophosphate compound and soot, the lubricating composition comprising a nitrogen-containing ashless dispersant that has a Functionality (F) of greater than 1.4.
 2. The lubricating composition of claim 1, wherein the nitrogen-containing ashless dispersant has a Functionality (F) of greater than 1.5.
 3. The lubricating composition of claim 1, wherein the nitrogen-containing ashless dispersant comprises a functionalized oil-soluble polymeric hydrocarbon backbone which has been derivatized with a nitrogen-containing nucleophilic reactant.
 4. The lubricating composition of claim 3, wherein the nitrogen-containing nucleophilic reactant is selected from an amine, amino-alcohol, amide, or mixture thereof.
 5. The lubricating composition of claim 3, wherein the nitrogen-containing nucleophilic reactant is an amine.
 6. The lubricating composition of claim 1, wherein the nitrogen-containing ashless dispersant comprises at least one polyalkenyl succinimide, which is the reaction product of a polyalkenyl substituted succinic anhydride and a polyamine.
 7. The lubricating composition of claim 1, wherein the nitrogen-containing ashless dispersant comprises at least one polyisobutylene succinimide.
 8. The lubricating composition of claim 1, wherein the nitrogen-containing dispersant is present in the lubricating composition at a level such as to provide a level of nitrogen of from 0.001 wt % to 15 wt %, by weight of the lubricating composition.
 9. The lubricating composition of claim 1, wherein the nitrogen-containing dispersant is present in the lubricating composition at a level such as to provide a level of nitrogen of from 0.05 wt % to 0.1 wt %, by weight of the lubricating composition.
 10. The lubricating composition of claim 1, wherein the lubricating composition comprises a base oil and one or more additives. 